Subpixel structure in a twisted nematic LCD. Credit: Lion_on_helium/MIPT Press Office

An international team of researchers has developed a new method to orient liquid crystals that could be used to increase the viewing angle of liquid-crystal displays (LCDs).

Researchers from Russia, France and Germany found that by adding one methylene group to the side chain of the polymer, they could switch the liquid crystal orientation, which is crucial for most applications of LCDs. This effect could be used to design LCDs with improved viewing angles by using a multidomain technology that works by orienting subpixels of one color in different directions.

“This is first and foremost a fundamental study exploring the mechanisms of liquid crystal orientation,” Dimitri Ivanov, the head of the Laboratory of Functional Organic and Hybrid Materials at the Moscow Institute of Physics and Technology, said in a statement. “That said, we expect that these mechanisms might have applications in new LCD technology.”

The researchers worked with liquid-crystal polymers—poly(di-n-alkylsiloxanes0 (PDAS)—composed of long molecules with chainlike repetitive structure. Each molecule is a chain containing alternating silicon and oxygen atoms.

The team found that a slight variation in the structure of the polymers drastically altered their orientation on the substrate, allowing them to switch the liquid-crystal orientation.

It was also discovered that the liquid-crystal orientation varied depending on side-chain length the needlelike polymer superstructures known as lamellae co-aligned with the Teflon grooves.

This could be achieved using a multidomain technology that works by orienting subpixels of one color in different directions. As a result, the pixels compensate one another when the display is viewed at an angle, improving color rendition

This technology is considerably simpler and cheaper than other multidomain approaches that are currently used.

The majority of solids are crystals, where molecules or atoms form an ordered 3D structure. However, unlike solids, liquids lack the internal long-range order, but can flow. Matter in a liquid-crystal state has properties that are intermediate between those of liquids and crystals—it possesses both the molecular order and the ability to flow.

The properties of a liquid crystal material depends on the direction. For example, polarized light propagates in a liquid crystal at different speeds along different directions. In an electric or magnetic field, the orientation of liquid crystals can also rapidly change in a phenomenon called the Fréedericksz transition.

Liquid crystal’s feature images that are generated by the changing in the intensity of light in each pixel through an electric field, which realigns liquid crystals, enabling LCs to be widely used in electronic display.

The most common liquid crystal configuration is where there are rod-shaped thermotropic liquid crystals that can adopt a twisted configuration by using special aligning substrates.

Each pixel in a color LCD consists of a red, green and blue subpixel and by varying their intensities, any color can be displayed.

A subpixel in a twisted nematic-based LCD consists of a light source, a color filter, two polarizers, and an LC cell between two glass plates with electrodes.

If the liquid crystals were not there, no light would pass through the cell due to the light that is let through by the vertical polarizer is blocked by the horizontal polarizer before reaching the color filter.